1. Field of the Invention
Crystalline polyimidesiloxanes are especially useful in electronic applications because of their low water absorption and good adhesion to various substrates used in electronic applications such as printed circuits, computer chips and the like.
2. Prior Art
Polyimides with a low dielectric constant and low absorption of water can be achieved by use of fluorinated monomers such as disclosed by L. M. Ruiz in Proc. 3rd SAMPE Electronic Conference (1989), page 209, and/or by the use of siloxane monomers, such as disclosed by Stokley et al in the same SAMPE conference at page 224. The fluorinated polyimides have high coefficient of thermal expansion (a CTE of over 40 ppm/C and high Young's modulus (over 350,000 psi). These two properties result in high residual stress when the fluorinated polyimides are used for coating on low CTE electronic substrates, such as silicon and alumina. These results are disclosed by Schuckert et al in "The Revolution of Packaging Dielectrics", in P. Bindra and R. A. Susko in the Proc. Symp. Packaging of Electronic Devices, Electrochem. Soc. Inc. (1989), page 116.
Some high performance polyimidesiloxanes have recently emerged as an important class of electronic polymers, such as disclosed by me in "Polyimidesiloxanes: State of the Material and Technology", in C. P. Wong, "Polymers for Electronics and Photonics Applications", Academic Press, to be published in 1990. Other disclosures occur in my papers in J. Electronics Material, Volume 18(2), (1989) at page 313; and Proc. 39th Electronic Components Conference, CHMT, (1989), page 896 and references disclosed therein. These polyimidesiloxanes usually possess a glass transition temperature (Tg) of higher than 200.degree. C., a dielectric constant equal to or lower than 3.0 to 2.6, and a Young's modulus no more than 150,000 psi at room temperature for low stress coating applications. However, all these polyimidesiloxanes are amorphous materials and they absorb a certain amount of water (0.6 to 1.0% maximum) in proportion to their imide contents.
My U.S. Pat. No. 4,558,110 discloses a crystalline silicone-imide block copolymer comprising at least one imide-disiloxane block, wherein the imide portion of said imide-disiloxane block has a symmetrical aromatic radical as its nucleus, and at least one polydiorganosiloxane has at least about five siloxy units.
The purpose of this invention is to provide new low dielectric polyimidesiloxanes which exhibit very low water absorption, such as a maximum of about 0.5 weight percent.